Beetween the tags <list id="maps"> and </list> you need to have a row for each face you have put IN THE SAME DIRECTORY.

The XXXXXXXXXX stands for a number that is the UNIQUE ID of the player (search on the forum or on Google for this), and
you've to follow these simple rules:
- the photo of the player need to be a PNG file named XXXXXXXXXX.png
- the file HAVE TO BE in the same directory of the file config.xml

For example if Lionel Messi unique id was 12345678 (is wrong, but just an example ...) you need to:
- rename the file with his face as 12345678.png
- put it in the directory Documents\Sports interactive\Football Manager 2012\graphics\faces\Barcelona\
- create (or modify) the file config.xml in the same directory adding the line
<record from="12345678" to="graphics/pictures/person/12345678/portrait"/>

I know that all this could sound like an alien thing ... if so please download any facepack and take a look